The invention relates to coating and molding compositions containing specific siloxanes defined hereinafter to improve spreading and to increase lubricity. The invention also relates to the use of specific siloxanes defined hereinafter to improve the spreadability and increase the lubricity of coating and molding compositions.
It is known to add siloxanes to paints to facilitate spreading and to obtain higher scratch resistance and lubricity. This addition of low molecular weight dimethylpolysiloxanes and methylphenylpolysiloxanes is described in German Pat. Nos. 11 11 320 and 10 92 585. It is further known that polyoxyalkylene modified dimethylpolysiloxanes can be used to obtain similar effects. In this case, the polyoxyalkylene radical serves to improve compatibility in the coating materials (Goldschmidt Informiert, 7/1982, No. 56, p. 2; 6th Fatipec Congress, 1962, p. 332).
However, the known dimethylpolysiloxanes lead in many cases to turbidity in unpigmented coating materials and to poor spreading, which becomes apparent in so-called graining. If the molecular weights of these pure polydimethylsiloxanes are too high, strong disturbances occur in the coating materials, which appear as craters or so-called fisheyes (Wagner/Sarx, Lackkunstharze (1971), p. 166).
The aforementioned polymethylphenylsiloxanes are in most cases highly compatible in coating materials and display good spreadability improving properties, but they are not effective in increasing the scratch resistance.
The aforementioned polyoxyalkylene modified polysiloxanes are highly compatible in many coating compositions, but lead to an undesirable structural configuration, which in roller application of such coating compositions, as is customary in so-called "coil coating", results in a grooved structure. Polyoxyalkylene modified polysiloxanes also are not thermally stable, which particularly becomes clearly apparent at drying temperatures above 150.degree. C. This thermal instability results after the decomposition of the polyoxyalkylene chain in incompatible reaction products and becomes noticeable in a deteriorating intermediate layer adhesion, which may go so far that the second layer may be readily pulled off the first layer. In such a case, the siloxanes act as release agents (Wagner/Sarx, Lackkunstharze (1971), p. 166).